To the Editor: Alexander et al. (Aug. 23 issue)(1) report findings from a prospective, multicenter gene-expression classifier validation study that raises several questions. For the 265 indeterminate fine-needle aspirates they tested, the gene-expression classifier had a sensitivity of 92%, a specificity of 52%, a positive predictive value of 47%, and a negative predictive value of 93%. Why the observed reduction in the performance of the gene-expression classifier, which was reported in their earlier study to have a sensitivity of 100% and a specificity of 73.3%?(2) With a high negative predictive value and a low positive predictive value, the gene-expression classifier . . .